Structure and Function of Bacterial Cells

Bacteria Overview

• Prokaryotic microorganisms lacking internal membranous organelles like a nucleus, mitochondria, or lysosomes.
• Exhibit diverse shapes: bacilli (rod-shaped), cocci (spherical/ovoid), and spirilla (spiral/wavy forms).

Bacterial Structure

• Cytoplasm: Dense medium containing ribosomes, metabolic enzymes, and storage granules for glycogen, lipids, or phosphates.
• Nucleoid: Contains a single, circular DNA strand (double-helical) holding 3,000 - 6,000 genes, located within the cytoplasm.
• Plasmid: Small circular DNA molecule carrying genes separate from the main chromosome, often involved in antibiotic resistance.
• Capsule: A thick gelatinous layer surrounding some bacteria, composed of polysaccharides, providing defense against the immune system and increasing virulence.
• Flagella: Motility structures made of three parts (Basal granule, hook, filament) anchored to the cell membrane and cell wall.
• Pili: Tubular protein extensions used for bacterial clumping and genetic material exchange during conjugation.

Gram Staining and Cell Wall Structure

• Gram-Positive: Characterized by a thick peptidoglycan layer outside the plasma membrane; susceptible to penicillin which disrupts cell wall production.
• Gram-Negative: Comprised of a thin peptidoglycan layer and a second outer layer of carbohydrates and lipids, providing resistance to certain antibiotics.

Bacterial Reproduction

• Transverse Binary Fission: Asexual reproduction process involving DNA replication and division into two identical cells by septum formation; can occur rapidly under optimal conditions, potentially producing up to 250,000 cells in 6 hours.

Horizontal Gene Transfer Mechanisms

• Transformation: Uptake of fragments of DNA from a disrupted bacteria by another bacteria.
• Conjugation: Direct transfer of genetic material between two bacteria via a sex pilus.
• Transduction: Transfer of genetic material mediated by bacteriophages (viruses that infect bacteria).

Key Facts

• Penicillin is specifically effective against Gram-positive bacteria due to its impact on peptidoglycan production.